Plants occupy nearly every habitat on earth, but scientists do not have a full understanding of the adaptive mechanisms plants use to survive extremely stressful environments. In this study, researchers used genomics to examine the genes that are regulated by the stress hormone abscisic acid (ABA). The researchers looked at how these genes differ between plants that are sensitive or resistant to high levels of salt in the soil. The study found that the specific gain or loss of regulatory DNA sequences in plant genes led to differences in how stress regulates those genes. This explains why ABA accelerates growth in one member of the mustard family, Schrenkiella parvula.
Understanding the way stress regulates how plants grow will help scientists breed and engineer bioenergy crops that grow on marginal land. This study reveals that stress hormones do not always act as growth inhibiting signals. This opens the possibility of rewiring these responses in crops to limit the negative effects of environmental stress on plant yields.
The plant hormone ABA is a critical component of the stress acclimation mechanism in many plants. Plants produce ABA in response to a wide array of water associated stresses such as drought, salinity, cold and heat. As ABA levels rise, a plant’s growth can slow due to the inhibition of processes such as cell division and elongation. In this study, researchers from Stanford University, Louisiana State University, and the Salk Institute compared the response of stress sensitive and stress tolerant species, so called “extremophytes,” which can tolerate excessively high levels of environmental stress. While one of these halophytes exhibits similar responses to ABA as stress sensitive species, the species Schrenkiella parvula shows growth acceleration due to an enhancement of cell elongation in the roots.
For this study, the researchers used RNAseq-based transcriptomic characterization of these species as well as DNA Affinity Purification and Sequencing (DAP-seq) to establish the first cross-species gene regulatory network for stress response based on direct measurements of protein-DNA binding landscapes. The comparison of the regulatory networks between species identified targets of ABA signaling that are conserved across species while contrasting these networks allows us to identify a subnetwork that was highly divergent in Schrenkiella parvula and controlled the biosynthesis of the growth hormone auxin. Loss of the regulatory connections between ABA and auxin provides a mechanism to explain why ABA has lost its growth inhibitory effects in this extremophyte.
Funding for this research was provided by the Department of Energy Office of Science, Biological and Environmental Research program, the Carnegie Institution for Science Endowment, the National Science Foundation, the Rural Development Administration of South Korea, and the HHMI-Simons Faculty Scholar program.